1. Field of the Invention
This invention relates to a process for direct oxidation of hydrocarbons, particularly lower alkanes and benzene, to acids by dioxygen under mild temperature conditions using certain metallic or metallic salt catalysts, particularly metallic palladium or platinum or RhCl.sub.3 or CuSO.sub.4 metallic salt catalysts. Turnovers in excess of 1000 for acetic acid formation from ethane and in excess of 100 for formic acid formation from methane have been observed at reaction temperatures below about 100.degree. C.
2. Description of Related Art
A number of processes for oxidation of unsaturated hydrocarbons are known, for example: U.S. Pat. No. 2,926,191 teaching oxidation of C.sub.4 -C.sub.6 paraffins with O.sub.2 without any catalyst to produce acetic acid; U.S. Pat. No. 4,739,107 teaching reaction of an unsaturated hydrocarbon, alcohol and CO over Pd or Pt at 20.degree. to 200.degree. C., with O.sub.2 optionally present, to form dicarboxylate esters; U.S. Pat. Nos. 4,681,707 and 4,665,213 teaching similar reactions as the U.S. Pat. No. 4,739,107 with the additional requirement of the catalyst including copper, and teaching substitution of water for the alcohol reactant to produce the corresponding carboxylic acids; U.S. Pat. No. 4,414,409 teaching reaction of an unsaturated hydrocarbon, carbon monoxide and a hydroxylic compound in the presence of a catalyst of an organic phosphine liganded palladium compound and perfluorosulfonic acid to produce corresponding acids and esters; U.S. Pat. No. 3,876,694 teaching oxycarbonylation of olefins to form corresponding acids in a non-aqueous medium using a catalyst system of aluminum, boron or an alkaline earth metal and a compound of palladium which is soluble in the reaction medium; and U.S. Pat. No. 4,469,886 teaching hydrocarboxylation of propylene with carbon monoxide and water to produce isobutyric acid using a catalyst of palladium, a phosphoamine promoter ligand compound and a hydrogen halide.
Catalytic oxidation of saturated hydrocarbons, such as alkanes, requiring C-H activation is a very different and difficult chemical challenge, and one of great practical importance. The lower alkanes of 1 to about 6 carbon atoms are most abundant and least reactive of the alkanes, with methane being the most abundant and least reactive, having a C-H bond energy of 104 kcal/mol, with ethane being second in both categories. A number of processes have been described for such oxidations but they each suffer from requirement of high temperature and/or low turnovers of less than about 10: Baerns, M., van der Wiele, K., and Ross, J. R. H., Methane Activation--A Bibliography, Catal. Today, 4, 471-494, (1989); Pitchai, R. and Klier, K., Partial Oxidation of Methane, Catal. Rev.-Sci. Eng., 28(1), 13-88, (1986); Kung, H. H., Selective Oxidation Catalysis II, Stud. Surf. Sci. Catal., 45, 200-226, (1989); Hunter, N. R., Gesser, H. D., Morton, L. A., Yarlagadda, P. S., and Fung, D. P. C., Methanol Formation at High Pressure by the Catalyzed Oxidation of Natural Gas and by the Sensitized Oxidation of Methane, Appl. Catal., 57, 45-54, (1990); Burch, R., Squire, G. D., Tsang, S. C., Direct Conversion of Methane into Methanol, J. Chem. Soc., Faraday Trans. 1, 85(10), 3561-3568, (1989); Kowalak, S. and Moffat, J. B., Partial Oxidation of Methane Catalyzed by H-Mordenite and Fluorinated Mordenite, Appl. Catal., 36, 139-145, (1988); Stolarov, I. P., Vargaftik, M. N., Shishkin, D. I., and Moiseev, I. I., Oxidation of Ethane and Propane With Co(II) Catalyst, J. Chem. Soc., Chem. Commun., 938-939, (1991); Vargaftik, M. N., Stolarov, I. P., and Moiseev, I. I., Highly Selective Partial Oxidation of Methane to Methyl Trifluoroacetate, J. Chem. Soc., Chem. Commun., 1049-1050, (1990); Herron, N., The Selective Partial Oxidation of Alkanes Using Zeolite Based Catalysts, New J. Chem., 13, 761-766, (1989); and Lyons, J. E., Ellis, Jr., P. E., and Durante, V. A., Active Iron Oxo Centers for the Selective Oxidation of Alkanes, Stud. Surf. Sci. Catal., 67, 99-116, (1991). The Lyons, et al reference, supra, strives to achieve a one-step route to oxidation of lower alkanes to alcohols using iron oxo complexes as catalysts. The oxidation of lower alkanes with O.sub.2 catalyzed by azide-activated Group IV(a) to VIII transition metal coordination complexes is taught by U.S. Pat. No. 4,895,682. One well known disadvantage of such coordination complexes is their tendency to degrade under oxidative conditions. Mercury catalyzed oxidation of methane to methanol under mild conditions is taught by Periana, R. A., Taube, D. J., Evitt, E. R., Loffler, D. G., Wentrcek, P. R., Voss, G. and Masuda, T., A Mercury-Catalyzed, High-Yield System for the Oxidation of Methane to Methanol, Science, 259, pp. 340-343, (1993). Low temperature reaction of methane with chlorine in the presence of platinum chlorides and in-situ hydrolyzation of the formed methyl chloride to methanol is taught by Horvath, I. T., Cook, R. A., Millar, J. M. and Kiss, G., Low-Temperature Methane Chlorination with Aqueous Platinum Chlorides in the Presence of Chlorine, Organometallics, 12, pp. 8-10, (1993). Catalytic oxidation of ethane to acetic acid at temperatures above about 250.degree. C. using promoted vanadium oxide catalysts is taught by Merzouki, M., Taouk, B., Monceaux, L., Bordes, E. and Courtine, P., Catalytic Properties of Promoted Vanadium Oxide in the Oxidation of Ethane in Acetic Acid, New Developments in Selective Oxidation by Heterogeneous Catalysis; Studies in Surface Science and Catalysis, Ruiz, P and Delmon, B., Eds., Vol. 72, pp. 165-179, (1992).
Metal-catalyzed water-gas-shift reactions are known as exemplified by: Thomas, C. L., Catalytic Processes and Proven Catalysts, Academic, New York, 104, (1970); Happel, J., Study of Knietic Structure Using Marked Atoms, Catal. Rev., 6,(2), 221-260, (1972); Laine, R. M., and Wilson, Jr., R. B., Recent Developments in the Homogeneous Catalysis of the Water-Gas Shift Reaction, in Aspects of Homogeneous Catalysis, Ugo, R., Ed., D. Reidel, Dordrecht, 5, 217-240, (1984); and Ford, P. C., The Water Gas Shift Reaction: Homogeneous Catalysis by Ruthenium and Other Metal Carbonyls, Acc. Chem. Res., 14, 2, 31-37, (1981).
The catalytic formation of hydrogen peroxide from dihydrogen and dioxygen using palladium on absorbent carbon is taught by U.S. Pat. No. 4,681,751. The selective oxidation of hydrogen to hydrogen peroxide by palladium on a hydrophobic support is taught by Fu, L., Chuang, K. T. and Fiedorow, R., Selective Oxidation of Hydrogen to Hydrogen Peroxide, New Developments in Selective Oxidation by Heterogeneous Catalysis; Studies in Surface Science and Catalysis, Ruiz, P. and Delmon, B., Eds., Vol. 72, pp 33-41, (1992).
The oxidation of 2-propanol to acetone by dioxygen has been reported by Nicoletti, J. W. and Whitesides, G. M., Liquid-Phase Oxidation of 2-Propanol to Acetone by Dioxygen Using Supported Platinum Catalysts, J. Phys. Chem., 93, 759-767, (1989).
Metal catalyzed oxidation of alcohol to carboxylic acid requiring a divalent platinum complex for the initial oxidation step is taught by Sen, A. and Lin, M., A Novel Hybrid System for the Direct Oxidation of Ethane to Acetic and Glycolic Acids in Aqueous Medium, J. Chem. Soc., Chem. Commun., 6, 508-510, (1992) and Sen, A., Lin, M., Kao, L. C., and Hutson, A. C., J. Am. Chem. Soc. 114, 6385, (1992).
The partial oxidation of methane in a motored engine at 650.degree. to 800.degree. C. and under compression of 20/1 to 60/1 without any catalyst to form small amounts of oxygenated products is taught by U.S. Pat. No. 2,922,809.
The formation of acetic acid from methane and carbon dioxide and the formation of acetaldehyde from methane and carbon monoxide by addition reactions in the presence of a metal catalyst such as palladium or platinum or their carbonates is taught by U.S. Pat. No. 1,916,041. It must be noted that there is no net oxidation in the reactions taught by the U.S. Pat. No. 1,916,041. Further, the addition reactions referred to in U.S. Pat. No. 1,916,041 are thermodynamically uphill and cannot proceed except to produce trace amounts of the products as set forth by Jones, W. D., Development of Catalytic Processes for the Synthesis of Organic Compounds the Involve C-H Bond Activation, Chap. 5, 113-148, Selective Hydrocarbond Activation, Principles and Progress, Edited by Davies, J. A., Watson, P. L., Greenberg, A. and Lichman, J. F., VCH, (1990).